Optical navigation device and failure identification method thereof

ABSTRACT

There is provided a failure identification method of an optical navigation device including the steps of: constructing a fixed noise map according to image frames captured by an image sensor; calculating a feature value of the fixed noise map; identifying whether the fixed noise map is uniform or not according to the feature value; and generating an alert signal when the fixed noise map is non-uniform for indicating failure of the optical navigation device.

BACKGROUND

1. Field of the Disclosure

This disclosure generally relates to an optical navigation device and,more particularly, to an optical navigation device and failureidentification method thereof operating based on the noise map.

2. Description of the Related Art

Images captured by an optical tracking engine generally include a fixednoise pattern, wherein said fixed noise pattern may be caused byphotodiodes of the image sensor, optical elements or the light sourceitself. In order to increase the accuracy of post-processing, the fixednoise pattern may be removed from the current image using algorithmaccording to a previously constructed noise map.

For example before shipment, it is able to illuminate an image sensor ofthe optical tracking engine with a uniform light source and recordnon-uniform positions of an outputted image to be served as apredetermined noise map. In actual operation, fixed noises can beeliminated using algorithm executed by a processor. In other words,conventionally said noise map is used to eliminate fixed noises in theprocess of image processing.

However, in the optical tracking system requiring high accuracy, inaddition to the defects existing in the device itself, the operatingenvironment may also cause the particle contamination of the opticaltracking system so as to form the fixed noise. Accordingly, the opticaltracking system is preferably able to identify whether failure may occurin the optical tracking engine according to the current image capturedin actual operation.

SUMMARY

Accordingly, the present disclosure further provides an opticalnavigation device and failure identification method thereof that mayconstruct a fixed noise map according to the image frames captured inoperation and use the fixed noise map as a basis of failureidentification. When the optical navigation device identifies accordingto the fixed noise map that the system may be failed, the user isinformed to remove the source that could possibly cause fixed noises.

The present disclosure provides an optical navigation device and failureidentification method thereof that may construct a fixed noise mapaccording to the current frame captured in operation and give an alertwhen identifying failure according to the fixed noise map.

To achieve the above object, the present disclosure provides an opticalnavigation device including an image sensor and a navigation processor.The image sensor is configured to successively output image frames. Thenavigation processor is configured to update a transition noise mapaccording to a first ratio of the transition noise map and a secondratio of a current frame, generate a fixed noise map when an updatecount reaches a counting threshold, and generate an alert signal when afeature value of the fixed noise map exceeds a feature threshold.

The present disclosure further provides a failure identification methodof an optical navigation device including the steps of: identifyingwhether a movement occurs; updating a transition noise map according toa first ratio of the transition noise map and a second ratio of acurrent frame when the movement occurs; generating a fixed noise mapwhen an update count reaches a counting threshold; and generating analert signal indicating failure of the optical navigation device when afeature value of the fixed noise map exceeds a feature threshold.

The present disclosure further provides a failure identification methodof an optical navigation device including the steps of: constructing afixed noise map according to image frames captured by an image sensor;calculating a feature value of the fixed noise map; identifying whetherthe fixed noise map is uniform or non-uniform according to the featurevalue; and generating an alert signal indicating failure of the opticalnavigation device when the fixed noise map is non-uniform.

In one aspect, the first ratio is preferably much larger than the secondratio.

In one aspect, the feature value may be a standard deviation or alocalized comparison of the fixed noise map.

In one aspect, the optical navigation device further includes an alertunit configured to represent an alert state according to the alertsignal, e.g. representing the alert state by displaying, sound,illumination and/or vibration.

In one aspect, the optical navigation device is further configured tocalculate a displacement according to a reference frame and the currentframe, and update the transition noise map only when the displacementexceeds a displacement threshold, wherein an initial transition noisemap of the transition noise map may be a predetermined ratio of aninitial image frame captured by the image sensor in a startup procedureor after a sleep mode ends.

In the optical navigation device and failure identification methodaccording to the embodiment of the present disclosure, when adisplacement obtained by the optical navigation device exceeds adisplacement threshold, a current frame captured by the image sensor isadded to a transition noise map with a predetermined ratio and the addedresult is then used to replace (i.e. update) the transition noise map.When the displacement is smaller than the displacement threshold, thecurrent frame is only used to calculate the displacement without beingused to update the transition noise map thereby improving theperformance of constructing the fixed noise map. When a predeterminedupdate count is reached, the navigation processor takes the transitionnoise map as a fixed noise map and identifies the uniformity of thefixed noise map. When the uniformity of the fixed noise map is poor, itmeans that the optical navigation device needs to be maintained suchthat an alert is given to inform the user so as to avoid misoperation ofthe optical navigation device.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages, and novel features of the present disclosurewill become more apparent from the following detailed description whentaken in conjunction with the accompanying drawings.

FIG. 1 shows a schematic block diagram of the optical navigation deviceaccording to an embodiment of the present disclosure.

FIG. 2 shows a flow chart of the failure identification method of anoptical navigation device according to an embodiment of the presentdisclosure.

FIG. 3 shows a schematic diagram of constructing a fixed noise map inthe optical navigation device according to the embodiment of the presentdisclosure.

FIG. 4 shows a flow chart of the failure identification method of anoptical navigation device according to another embodiment of the presentdisclosure.

DETAILED DESCRIPTION OF THE EMBODIMENT

It should be noted that, wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

Referring to FIG. 1, it shows a schematic block diagram of the opticalnavigation device 1 according to an embodiment of the presentdisclosure. The optical navigation device 1 is configured to construct afixed noise map indicating the noise amount of an operation environmentaccording to the image frames captured in operation, wherein said noisemay include the defects of the optical system itself and particlecontamination. The optical navigation device 1 then calculates a featurevalue of the fixed noise map for indicating uniformity of the fixednoise map, wherein the feature value may be a standard deviation or alocalized comparison of the fixed noise map, but not limited to. In thepresent disclosure, the noise map indicates a noise distribution in theimage frame captured by the optical navigation device 1 so that thenoise map and the image frame may have identical sizes and resolutions.

In one embodiment, the localized comparison (indicating uniformity U)may be defined as a calculation result of at least two pixel valueswithin a predetermined range around each pixel value G(x,y) in the fixednoise map, wherein the localized comparison may be represented byequation (I). For example in one embodiment, the uniformity U may be asum of absolute differences between each pixel value G(x,y) in the fixednoise map and at least one neighbor pixel value within a predeterminedrange around the pixel value G(x,y), but not limited thereto. Thefeature value may also be calculated by other conventional methods forcalculating the uniformity of a digital matrix.

$\begin{matrix}{{GR} = {\sum\limits_{x,y}{{{filter}\left( {x,y} \right)} \otimes {G\left( {x,y} \right)}}}} & (1)\end{matrix}$

Finally, the optical navigation device 1 identifies whether failure mayoccur according to the feature value and gives an alert, if failureoccurs, to inform the user to remove the source that could possiblycause the failure, e.g. cleaning or exchanging components.

Referring to FIG. 1 again, the optical navigation device 1 may include alight source 11, at least one light guide 12 (a lens shown herein as anexample), an image sensor 13, a navigation processor 14, a storage unit15, an input/output (I/O) unit 16 and an alert unit 17, wherein theimage sensor 13, navigation processor 14, storage unit 15 and I/O unit16 may be formed as a control chip. It should be mentioned that thecontrol chip may be implemented by software, hardware, firmware or anycombination thereof. In addition, the storage unit 15 may be disposedinside the navigation processor 14 and not limited to that shown in FIG.1.

In the present disclosure, the optical navigation device 1 may be movedon a work surface S, or the optical navigation device 1 has a fixedposition and the work surface S is moved with respect to the opticalnavigation device 1. In addition, the optical navigation device 1 mayfurther include a light control unit (not shown) configured to controlthe ON/OFF of the light source 11.

The light source 11 may be a coherent light source (e.g. laser), apartial coherent light source or an incoherent light source (e.g. lightemitting diode) which is configured to illuminate the work surface S forproviding reflected light impinge on the image sensor 13. However, ifthe ambient light is enough, the system light source 11 may not beimplemented and only the ambient light is used.

The light guide 12 is configured to improve the sensing efficiency ofthe image sensor 13. In addition, the optical navigation device 1 mayfurther include other light guide associated with the light source 11 soas to improve the emission efficiency thereof. In addition, only onelight guide may be used to achieve the effects mentioned above, and theshape and position of the light guide may be determined according todifferent applications and not limited to that shown in FIG. 1.

The image sensor 13 may include a sensing array 131 and ananalog-to-digital converter (ADC) 132. The sensing array 131 may includea plurality of light sensing elements, e.g. photodiodes arranged inmatrix so as to output electrical signals according to the sensed lightintensity (e.g. the intensity of reflected light from the work surfaceS). The ADC 132 converts the electrical signals to digital signals andoutputs the image frame IF. The image sensor 13 may successively outputthe image frame IF at a sensing frequency, wherein a value of thesensing frequency may be determined according to its application withoutparticular limitation.

The navigation processor 14 is configured to update a transition noisemap according to a first ratio of the transition noise map and a secondratio of a current frame, wherein the transition noise map is referredto the incomplete fixed noise map being temporarily stored in thestorage unit 15, and the current frame is referred to a latest imageframe captured by the image sensor 13. When an update count of updatingthe transition noise map reaches a counting threshold, the transitionnoise map is served as a fixed noise map by the navigation processor 14;i.e. the transition noise map becomes the fixed noise map after beingupdated by a plurality of times determined by the counting threshold.When a feature value of the fixed noise map exceeds a feature threshold,the navigation processor 14 generates an alert signal Sw (describedlater). In addition, the navigation processor 14 may further calculate adisplacement according to a reference frame and the current frame andupdates the transition noise map only when the displacement exceeds adisplacement threshold, wherein the method of calculating thedisplacement may use the correlation between image frames IF and sinceit is well known, details thereof are not described herein. In addition,according to different applications, the navigation processor 14 maystill update the transition noise map even though the displacement doesnot exceed the displacement threshold.

The storage unit 15 may be a computer readable medium and configured tosave the transition noise map, counting threshold, count value, featurethreshold, displacement threshold, reference frame, algorithminformation, area threshold, data required in operation and so on.

The I/O unit 16 is configured to wiredly or wirelessly communicate withoutside of the optical navigation device 1, e.g. transmitting thedisplacement to a host or transmitting the alert signal Sw to the alertunit 17. Since wired and wireless communication techniques are wellknown, details thereof are not described therein.

The alert unit 17 may be a display device, a speaker, an illuminationdevice and/or a vibrator, and configured to represent the alert stateaccording to the alert signal Sw by displaying, sound, illuminationand/or vibration, but the present disclosure is not limited thereto.Accordingly, when the alert state is represented, the user may clean orreplace associated component(s) to avoid misoperation.

Referring to FIG. 2, it shows a flow chart of the failure identificationmethod of an optical navigation device according to an embodiment of thepresent disclosure, which includes the steps of: constructing a fixednoise map according to image frames captured by an image sensor (StepS₂₂); calculating a feature value of the fixed noise map (Step S₂₄);identifying whether the fixed noise map is uniform or non-uniformaccording to the feature value (Step S₂₆); and generating an alertsignal for indicating failure of the optical navigation device when thefixed noise map is non-uniform (Step S₂₈).

Step S₂₂: In the present disclosure, the fixed noise map is constructedaccording to image frames captured in operation rather than beforeshipment. Accordingly, the navigation processor 14 may construct thefixed noise map according to the image frames IF successively outputtedby the image sensor 13, e.g. constructing the fixed noise map accordingto the method disclosed in U.S. Pat. No. 7,423,633 or 8,189,954, but notlimited thereto.

In one embodiment, the navigation processor 14 may calculate a sum of afirst ratio of a transition noise map and a second ratio of the imageframe IF, wherein the transition map is the one continuously updatedaccording to the image frames captured in operation of the navigationprocessor 14 before the fixed noise map has been constructed. When thetransition noise map is updated a plurality of times determined by acounting threshold, the transition noise map is served as the fixednoise map. In one embodiment, an initial transition noise map may be setas a predetermined ratio of an initial image frame captured by the imagesensor 13 during the startup or wakeup of the optical navigation device1, e.g. FIG. 3 showing an initial image frame IF_(—) _(initial) and aninitial transition noise map NM_(—) _(initial)=IF_(—) _(initial)/2,wherein said predetermined ratio is shown to be 0.5 herein, but thepresent disclosure is not limited thereto. In addition, as the presentdisclosure is to construct the fixed noise map according to the imageframes captured in operation, the first ratio is preferably much largerthan the second ratio such that more current operating components may beincluded in the noise map. For example, FIG. 3 shows that the firstratio may be 15/16 and the second ratio may be 1/16, but the presentdisclosure is not limited thereto.

Referring to FIG. 3 again, a transition noise map NM_(—) _(tran), may beobtained according to a sum of the first ratio of an initial transitionnoise map NM_(—) _(initial) and the second ratio of a current frame.Then, the transition noise map NM_(—) _(tran) is used to replace (e.g.update) the initial transition noise map NM_(—) _(initial), and a sum ofthe first ratio of the transition noise map NM_(—) _(tran) and thesecond ratio of a new current frame is calculated. By repeating theupdating process by a plurality of times determined by the countingthreshold, the fixed noise map is obtained.

Step S₂₄: Next, the navigation processor 14 calculates a feature valueof the fixed noise map according to a pre-stored algorithm forindicating the uniformity of the fixed noise map, wherein said featurevalue may be a standard deviation, a localized comparison or othervalues for indicating uniformity.

Step S₂₆: Next, the navigation processor 14 compares the feature valuewith a feature threshold, wherein when the feature value exceeds thefeature threshold the fixed noise map is identified being non-uniform,whereas when the feature value is smaller than the feature threshold,the fixed noise map is identified being uniform. A value of the featurethreshold may be determined according to the noise amount that can beendured by the navigation processor 14 such that it may be differentaccording to different applications and requirements.

Step S₂₈: Finally, when the fixed noise map is identified beingnon-uniform, the navigation processor 14 outputs an alert signal Sw tobe transmitted to the alert unit 17 via the I/O unit 16. The alert unit17 then informs the user with different ways according to its type thatthe optical navigation device 1 may be failed and required to bemaintained in order to avoid the misoperation. In the presentdisclosure, the alert unit 17 may be disposed independent from theoptical navigation device 1 without particular limitation, e.g.integrated in a host.

Referring to FIG. 4, it shows a flow chart of the failure identificationmethod of an optical navigation device according to another embodimentof the present disclosure, which further includes a movementidentification step S₂₀. Accordingly, the failure identification methodof this embodiment includes the steps of: identifying whether a movementoccurs (Step S₂₀); constructing a fixed noise map (Step S₂₂);calculating a feature value of the fixed noise map (Step S₂₄);identifying uniformity according to the feature value (Step S₂₆); andgenerating an alert signal (Step S₂₈); wherein the Steps S₂₄, S₂₆ andS₂₈ are identical to those of FIG. 2 and thus details thereof are notrepeated herein. In the Step S₂₆ of this embodiment, when a featurevalue of the fixed noise map exceeds (e.g. larger than or equal to) afeature threshold THf, the Step S₂₈ is entered so as to generate analert signal for indicating failure of the optical navigation device 1,whereas when a feature value of the fixed noise map is smaller than thefeature threshold THf, the Step S₂₀ is returned so as to update thereference frame with the current frame (Step S₂₀₉) and reconstruct afixed noise map for the next identification. Herein only the Steps S₂₀and S₂₂ are further explained.

Step S₂₀: In this step, the navigation processor 14 calculates adisplacement with respect to the work surface S and identifies whetherthe displacement exceeds (e.g. larger than or equal to) a displacementthreshold THd. No matter whether the displacement exceeds thedisplacement threshold THd or not, the navigation processor 14 transmitsthe displacement via the I/O unit 16, e.g. transmitting to a host. Inother words, besides for cursor control as an example, the displacementmay also be used to determine whether to update the noise map.

In this embodiment, the Step S₂₀ further includes the followingsub-steps. The image sensor 13 captures a reference frame (Step S₂₀₁).The image sensor 13 captures a current frame (Step S₂₀₃), wherein theimage sensor 13 may capture a current frame every sampling cycle. Thenavigation processor 14 calculates a displacement according to thereference frame and the current frame (Step S₂₀₅). The navigationprocessor 14 compares the displacement with a displacement threshold THd(Step S₂₀₇); when the displacement exceeds the displacement thresholdTHd, it means that a movement occurs and the step S₂₂ is entered;whereas when the displacement is smaller than the displacement thresholdTHd, is means that a movement does not occur and the reference frame isupdated by the current frame (Step S₂₀₉) and the process returns to theStep S₇₀₃ to allow the image sensor 13 to capture a new current frame.In this embodiment, the navigation processor 14 may calculate thedisplacement according to the correlation between the reference frameand the current frame. In addition, the reference frame and the currentframe may respectively be a differential image of a bright image, whichcorresponds to the turning on of the light source 11, and a dark image,which corresponds to the turning off of the light source 11. In thisembodiment, the sampling cycle may be determined according to the imagesensor 13 being employed.

Step S₂₂: This step further includes the following sub-steps. When themovement occurs, the navigation processor 14 updates a transition noisemap according to a first ratio of the transition noise map and a secondratio of the current frame (Step S₂₂₁). And when an update count reachesa counting threshold THc (Step S₂₂₃), a fixed noise map is generated andthe update count is reset to zero (Step S₂₂₅), wherein when the updatecount does not reach the counting threshold THc, the reference frame isreplaced by the current frame (Step S₂₀₉) and the process returns to theStep S₂₀₃ to allow the image sensor 13 to capture a new current frame.As mentioned above, an initial transition noise map NM_(—) _(initial) ofthe transition noise map may be a predetermined ratio of an initialimage frame captured in the startup or wakeup of the optical navigationdevice 1 and saved in the storage unit 15 as shown in FIG. 3. Thecounting threshold THc may be a fixed predetermined value saved in thestorage unit 15 or set by the user according to the operationconditions.

Next, the navigation processor 14 calculates a feature value of thefixed noise map (Step S₂₄) and compares the feature value with a featurethreshold THf (Step S₂₆), and generates an alert signal Sw when thefeature value exceeds (e.g. larger than or equal to) the featurethreshold THf (Step S₂₈).

In another embodiment, the Step S₂₀₇ in FIG. 4 may not be implemented;i.e. the navigation processor 14 may perform the Step S₂₂₁ of updatingthe transition noise map according to every current frame captured, notin a sleep mode, by the image sensor 13, wherein the definition of thesleep mode is well known and thus details thereof are not describedherein. In addition, in some applications the navigation processor 14does not identify whether the movement occurs again once a movement hasbeen identified; i.e. the navigation processor 14 only identifies thefirst movement and then performs the Step S₂₂₁ of updating thetransition noise map according to every current frame till the opticalnavigation device 1 stops operation, e.g. being turned off or entering asleep mode.

In another embodiment, the Step S₂₄ of calculating the feature value inFIG. 4 may be performed in Step S₂₀₃. For example, the navigationprocessor 14 may calculate the feature value of every current framecaptured by the image sensor 13, and the feature value is accumulated atthe same time the transition noise map is updated (i.e. S₂₀₇ issatisfied) whereas the feature value is not accumulated (e.g. abandoned)when the transition noise map is not updated (i.e. S₂₀₇ is notsatisfied). Accordingly, when the fixed noise map is obtained (i.e.S₂₂₅), the feature value of the fixed noise map is obtained at the sametime such that the Step S₂₄ may be omitted without being performed withan individual step. Said feature values may be stored in the storageunit 15.

In another embodiment, in the Step S₂₆ the area of individual noise inthe fixed noise map may further be identified so as to determine whetherto generate the alert signal Sw. For example, when areas of allindividual noise are smaller than an area threshold for performing thenavigation operation, the navigation processor 14 may not generate thealert signal Sw so as to ignore the negligible error; whereas when thearea of at least a part of individual noise is larger than the areathreshold, the navigation processor 14 generates the alert signal Sw. Inother words, the navigation processor 14 may determine whether to outputthe alert signal Sw according to the surface feature of the work surfaceS. It should be mentioned that the step of comparing the noise area andthe area threshold may be adapted to the Step S₂₆ of both FIGS. 2 and 4.The area threshold may be determined according to the detection accuracyrequired.

As mentioned above, the conventional optical tracking engine utilizesalgorithm to remove fixed noises in the image frame according to apreviously constructed predetermined noise map, but the conventionalmethod cannot eliminate the noise caused by operational environment inactual operation. Therefore, the present disclosure further provides anoptical navigation device (FIG. 1) and a failure identification methodthereof (FIGS. 2 and 4) that may construct a fixed noise map accordingto image frames captured in operation to accordingly identify whetherthe optical navigation device fails or not.

Although the disclosure has been explained in relation to its preferredembodiment, it is not used to limit the disclosure. It is to beunderstood that many other possible modifications and variations can bemade by those skilled in the art without departing from the spirit andscope of the disclosure as hereinafter claimed.

What is claimed is:
 1. An optical navigation device, comprising: animage sensor configured to successively output image frames; and anavigation processor configured to update a transition noise mapaccording to a first ratio of the transition noise map and a secondratio of a current frame, generate a fixed noise map when an updatecount reaches a counting threshold, and generate an alert signal when afeature value of the fixed noise map exceeds a feature threshold.
 2. Theoptical navigation device as claimed in claim 1, wherein the navigationprocessor is further configured to calculate a displacement according toa reference frame and the current frame, and the transition noise map isupdated only when the displacement exceeds a displacement threshold. 3.The optical navigation device as claimed in claim 1, wherein the firstratio is larger than the second ratio.
 4. The optical navigation deviceas claimed in claim 1, wherein an initial transition noise map is apredetermined ratio of an initial image frame captured by the imagesensor.
 5. The optical navigation device as claimed in claim 1, furthercomprising an alert unit configured to represent an alert stateaccording to the alert signal, wherein the alert unit represents thealert state by at least one of displaying, sound, illumination andvibration.
 6. The optical navigation device as claimed in claim 5,wherein the navigation processor is further configured to compare noiseareas of the fixed noise map with an area threshold so as to determinewhether to generate the alert signal.
 7. The optical navigation deviceas claimed in claim 1, wherein the feature value is a standard deviationor a localized comparison of the fixed noise map.
 8. The opticalnavigation device as claimed in claim 1, wherein the navigationprocessor is further configured to reset the update count when theupdate count reaches the counting threshold.
 9. The optical navigationdevice as claimed in claim 1, further comprising a storage unitconfigured to save the transition noise map, the counting threshold, thefeature threshold and the update count.
 10. A failure identificationmethod of an optical navigation device, comprising: identifying whethera movement occurs; updating a transition noise map according to a firstratio of the transition noise map and a second ratio of a current framewhen the movement occurs; generating a fixed noise map when an updatecount reaches a counting threshold; and generating an alert signalindicating failure of the optical navigation device when a feature valueof the fixed noise map exceeds a feature threshold.
 11. The failureidentification method as claimed in claim 10, wherein the first ratio islarger than the second ratio.
 12. The failure identification method asclaimed in claim 10, wherein an initial transition noise map is apredetermined ratio of an initial image frame captured by an imagesensor.
 13. The failure identification method as claimed in claim 10,further comprising: providing an alert unit configured to represent analert state according to the alert signal.
 14. The failureidentification method as claimed in claim 10, wherein the feature valueis a standard deviation or a localized comparison of the fixed noisemap.
 15. The failure identification method as claimed in claim 10,wherein when an update count of the transition noise map reaches acounting threshold, further comprises: resetting the update count.
 16. Afailure identification method of an optical navigation device,comprising: constructing a fixed noise map according to image framescaptured by an image sensor; calculating a feature value of the fixednoise map; identifying whether the fixed noise map is uniform ornon-uniform according to the feature value; and generating an alertsignal indicating failure of the optical navigation device when thefixed noise map is non-uniform.
 17. The failure identification method asclaimed in claim 16, wherein in the step of constructing a fixed noisemap, a sum of a first ratio of a transition noise map and a second ratioof the image frames is calculated.
 18. The failure identification methodas claimed in claim 16, wherein in the step of calculating a featurevalue, a standard deviation or a localized comparison of the fixed noisemap is calculated.
 19. The failure identification method as claimed inclaim 16, wherein the fixed noise map is non-uniform when the featurevalue exceeds a feature threshold; and the fixed noise map is uniformwhen the feature value is smaller than the feature threshold.
 20. Thefailure identification method as claimed in claim 16, furthercomprising: providing an alert unit configured to represent an alertstate according to the alert signal.